1. Field of the Invention
The present invention relates to a magnetoresistive film which indicates a resistance change in accordance with an external magnetic field strength, a magnetoresistive head for utilizing the resistance change of the magnetoresistive film to detect the external magnetic field strength, and an information regeneration apparatus for regenerating information recorded in a recording medium.
2. Description of Related Art
In recent years, with the spread of computers, a large amount of information has been handled in a daily manner. Such information is recorded on a recording medium by a large number of physical marks, and regenerated by an information regeneration apparatus for reading the mark on the recording medium to regenerate an electric regeneration signal.
A hard disk drive (HDD) is one of the information regeneration apparatuses, and is characterized in that a memory capacity is large and access speed to the information is fast. The HDD is provided with a magnetic disk as the recording medium whose surface is formed of a magnetic material, and a regeneration head for regenerating the information recorded on the magnetic disk. For the magnetic disk, a surface is magnetized for each micro area (one-bit region), and one bit of information is recorded in a form of a magnetization direction of the one-bit region. The regeneration head is disposed in the vicinity of the magnetic disk, and outputs the electric regeneration signal in accordance with a signal magnetic field Hsig generated from the magnetization of one-bit region of the magnetic disk to regenerate the information recorded on the magnetic disk.
As recording density of the magnetic disk continues to be enhanced year by year, an area of a one-bit region decreases with enhancement of the recording density, and the signal magnetic field Hsig generated from the one-bit region is weakened. Therefore, the regeneration head for outputting a large regeneration signal is necessary even for this weak signal magnetic field Hsig. As the magnetic head for outputting the large regeneration signal, a spin valve magnetoresistive head which is a magnetoresistive head utilizing a giant magnetoresistive (GMR) effect starts to be put to practical use in earnest. The spin valve magnetoresistive head will be hereinafter referred to as a SVMR head.
The SVMR head is provided with a spin valve magnetoresistive film as a multilayered film including a free magnetic layer whose magnetization direction changes in accordance with the signal magnetic field Hsig or another external magnetic field, a nonmagnetic middle layer formed adjacent to the free magnetic layer and provided with conductivity, a pinned magnetic layer formed adjacent to the nonmagnetic middle layer and provided with a magnetization direction fixed in a predetermined direction, and an antiferromagnetic layer formed adjacent to the pinned magnetic layer and constituted of an antiferromagnetic material for fixing the magnetization direction of the pinned magnetic layer. For the magnetoresistive film, sheet resistance xcfx81/t changes with relative angle changes of the magnetization directions of the free magnetic layer and pinned magnetic layer. When the magnetization directions of both layers are matched with each other in opposite directions, the sheet resistance xcfx81/t of the magnetoresistive film is maximized. When the magnetization directions of both layers are matched with each other in the same direction, the sheet resistance xcfx81/t is minimized. Therefore, by knowing the sheet resistance xcfx81/t of the magnetoresistive film, conversely, magnitude and direction of the external magnetic field can be known. A difference between a maximum value and a minimum value of the sheet resistance xcfx81/t will be hereinafter referred to as resistance change xcex94xcfx81/t.
The magnetoresistive film is provided with a pair of electrode terminals, and during operation a sense current is passed to the magnetoresistive film from the pair of electrode terminals. While the sense current flows, and when the SVMR head is relatively moved in the vicinity of a magnetic disk, an electric resistivity of the magnetoresistive film successively changes in accordance with the signal magnetic field Hsig from the magnetic disk, and a regeneration signal provided with an output voltage represented by a product of the electric resistivity and sense current value is outputted. The output of the regeneration signal of the SVMR head is substantially proportional to the resistance change xcex94xcfx81/t. In general, since the spin valve magnetoresistive film has a large resistance change xcex94xcfx81/t, the SVMR head outputs a high-output regeneration signal.
As one measure for obtaining a higher output from the SVMR head, there is proposed reduction of a height (length in a direction perpendicular to a surface opposite to the magnetic disk) of the magnetoresistive film. By reducing the height, a sectional area of a conductive path for passing the sense current decreases, the resistance change xcex94xcfx81/t increases, and the large-output regeneration signal is obtained.
However, since the magnetization direction of the pinned magnetic layer is fixed in the height direction, simply with the reduction of the height, a diamagnetic field of the pinned magnetic layer increases, and the fixing of the magnetization of the pinned magnetic layer is weakened. When the magnetization fixing is weakened, an angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer of the magnetoresistive film largely deviates from an ideal angle of 90 degrees. With such an angle deviating state, the resistance of the magnetoresistive film fails to linearly respond to a change of the signal magnetic field Hsig, and symmetry of SVMR head regeneration waveform is deteriorated with respect to a positive/negative signal magnetic field Hsig. Moreover, the deterioration of symmetry results in a decrease of a dynamic range on either the positive or negative side of the output voltage, and a substantial regeneration output decreases.
In order to decrease the diamagnetic field, known is a magnetoresistive film constituted of a laminated ferri-film in which the pinned magnetic layer is provided with a three-layer structure including a first soft magnetic layer, a second soft magnetic layer, and an antiparallel coupling middle layer, held between the first and second soft magnetic layers, for coupling the magnetizations of the soft magnetic layers to each other substantially in parallel or in opposite directions. In the laminated ferri-film, since the respective magnetizations of the first and second soft magnetic layers are directed and fixed in the opposite directions, the diamagnetic field is weak, and influence of the external magnetic field is hardly exerted, so that even when the height is reduced, the magnetization direction is firmly fixed. Therefore, by employing the laminated ferri-film in the pinned magnetic layer, the high output of the SVMR head can be obtained.
In order to obtain a much higher output from the SVMR head, for example, it is known that thickness of the free magnetic layer or the nonmagnetic middle layer is preferably reduced. This is because by forming these layers to be thin, an excess shunt current flowing through these layers and not contributing to a magnetoresistive effect is depressed and the resistance change xcex94xcfx81/t increases.
However, the magnetization of the free magnetic layer of the magnetoresistive film is given, from the magnetization of the pinned magnetic layer, an interlayer coupling field Hin attributed to interlayer coupling of these magnetizations, and with reduction of the thickness of the free magnetic layer or the nonmagnetic middle layer, this interlayer coupling field Hin increases. Since the interlayer coupling field Hin allows the angle formed by the magnetization directions of the free magnetic layer and pinned magnetic layer to deviate from the ideal angle of 90xc2x0, with an increase of the interlayer coupling field Hin, the substantial regeneration output of the SVMR head decreases. Particularly, when the pinned magnetic layer is constituted of a ferri-pin, the interlayer coupling field Hin increases to exceed 1.6 kA/m, and raises a problem.
The present invention has been developed in consideration of the aforementioned situations, and an object thereof is to provide a magnetoresistive film in which an interlayer coupling field Hin is minimized and a large regeneration output is produced, a magnetoresistive head, and an information regeneration apparatus.
To attain the aforementioned object, according to the present invention, there is provided a magnetoresistive film which is a multilayered film including: an underlayer; an antiferromagnetic layer formed on the underlayer; a pinned magnetic layer having magnetization whose direction is fixed by the antiferromagnetic layer; and a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field, and which indicates a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer.
In the magnetoresistive film, the pinned magnetic layer comprises a first soft magnetic layer and a second soft magnetic layer formed of soft magnetic materials and an antiparallel coupling middle layer, formed between the soft magnetic layers, for coupling the magnetizations of the soft magnetic layers to each other in opposite directions.
For the magnetoresistive film of the present invention, in a first magnetoresistive film, the antiferromagnetic layer comprises an ordered-form antiferromagnetic material including Mn, and the underlayer comprises a metal selected from the group consisting of Ru, Os, Re, Tc, Cd, Ti, Zn, Al, Au, Ir, Pd, Pt, Rh, Ag, Nb, Mo, W, V, and xcex1-Ta or an alloy including an element of the selected metal.
In the first magnetoresistive film of the present invention, the underlayer comprises Ru or an alloy including Ru, instead of the metal selected from the group or the alloy including the selected metal element in some cases.
Moreover, in the first magnetoresistive film of the present invention, the antiferromagnetic layer comprises a material containing 55 atom % or less of Mn and including an element selected from an element group consisting of Pd, Pt, Ru, Rh, Ir, Au, and Ni in some cases.
In general, as the antiferromagnetic material constituting the antiferromagnetic layer of the magnetoresistive film, the ordered-form antiferromagnetic material including Mn as described above is employed in many cases.
Moreover, as described in the related art, in general, for the magnetoresistive film, when the pinned magnetic layer has a multilayered structure including the soft magnetic layer and antiparallel coupling middle layer, the large regeneration output is produced, but the interlayer coupling field Hin also easily indicates a large value, and with the increase of the interlayer coupling field Hin the regeneration output decreases.
On the other hand, for the first magnetoresistive film of the present invention, since the pinned magnetic layer has the multilayered structure, and the appropriate material is selected as the underlayer material to constitute a substrate of the antiferromagnetic layer, as described later in an embodiment, a magnitude of the interlayer coupling field Hin is minimized and a large regeneration output is produced.
For the magnetoresistive film of the present invention, in a second magnetoresistive film, the antiferromagnetic layer comprises an ordered-form antiferromagnetic material including Mn, and is adjacent to the underlayer by a closest surface of a crystal of the antiferromagnetic material, the underlayer is adjacent to the antiferromagnetic layer by the closest surface of the crystal of a substrate material constituting the underlayer, and a ratio of a closest interatomic distance of the substrate material to the closest interatomic distance of the antiferromagnetic material is in a range of 0.92 to 1.08.
In the second magnetoresistive film of the present invention, the underlayer comprises Ru or an alloy including Ru in some cases.
Moreover, in the second magnetoresistive film of the present invention, the antiferromagnetic layer comprises a material containing 55 atom % or less of Mn and including an element selected from an element group consisting of Pd, Pt, Ru, Rh, Ir, Au, and Ni.
For the second magnetoresistive film, since the pinned magnetic layer is provided with the multilayered structure, and the material having the appropriate closest interlayer distance is selected as the material of the underlayer as the substrate of the antiferromagnetic layer, as described later in the embodiment, the magnitude of the interlayer coupling field Hin is minimized and the large regeneration output is produced.
To attain the aforementioned object, according to the present invention, there is provided a magnetoresistive head comprising a magnetoresistive film which is a multilayered film including: an underlayer; an antiferromagnetic layer formed on the underlayer; a pinned magnetic layer having magnetization whose direction is fixed by the antiferromagnetic layer; and a free magnetic layer having magnetization whose direction changes in accordance with an external magnetic field, and which indicates a magnitude of resistance in accordance with an angle formed by the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. The magnetoresistive head detects the magnitude of the resistance of the magnetoresistive film to detect a strength of the external magnetic field.
For the magnetoresistive head of the present invention, a first magnetoresistive head comprises the first magnetoresistive film of the present invention as the magnetoresistive film.
For the magnetoresistive head of the present invention for attaining the object, a second magnetoresistive head comprises the second magnetoresistive film of the present invention as the magnetoresistive film.
Since the magnetoresistive head of the present invention employs the magnetoresistive film of the present invention as the magnetoresistive film, the pinned magnetic layer is provided with the multilayered structure, further the interlayer coupling field Hin is minimized, and the regeneration output is large.
In order to attain the object, according to the present invention, there is provided an information regeneration apparatus which comprises a magnetic head, disposed in the vicinity of or in contact with a magnetic recording medium on which information is recorded in accordance with a magnetization direction, for detecting magnetization directions of respective points of the magnetic recording medium, and regenerates the information in accordance with the magnetization directions of the respective points of the magnetic recording medium detected by the magnetic head.
For the information regeneration apparatus of the present invention, a first information regeneration apparatus comprises the first magnetoresistive head of the present invention as a magnetic head.
For the information regeneration apparatus of the present invention for attaining the object, a second information regeneration apparatus comprises the second magnetoresistive head of the present invention as the magnetic head.
For these information regeneration apparatuses of the present invention, since the magnetoresistive head of the present invention is employed as the magnetic head, the regeneration output is large, and the apparatuses are suitable for regeneration of the information from a high-density recorded magnetic disk.